I am currently lvl 13, thought of starting to skill up, so got everything around 20-30 (Scavenging, Underworld trading and armortech).
Before i did this, i probably had like 2k credits. I then sent my companion continuously on gathering missions, as i was doing flashpoints, and then i hit level 14, go to the trainer, BAM you haz no gold to buy new talents.
So yes bit expensive imo
I'd like to get 10-20k credits like people are saying they have ... quests i guess ?